Background: Colorectal cancer (CRC) is one of the most common cancers. Family history is an important risk factor; first-degree relatives (FDRs) are most at risk. Studies are needed to determine the screening behavior of FDRs and factors affecting their health behaviors. Objective: The purpose of this study was to investigate the screening behaviors, health beliefs, and related factors of FDRs (parent, sibling, or child) of CRC patients undergoing treatment. Methods: A cross-sectional design was used with 400 FDRs of patients undergoing treatment at 2 hospitals in Turkey. Data were collected using the Colorectal Cancer Risk Questionnaire and the Turkish Colorectal Cancer Health Belief Model Scale. Results: A slight majority of the participants were male (51.3%), with a mean of age 37.7 years. The rate of having at least 1 colonoscopy in FDRs was 22.2%. First-degree relatives reported high perceived confidence-benefits scores on average (mean, 48.4 +/- 5.2) and high perceived barrier scores on average (mean, 15.5 +/- 3.8). Health motivation of FDRs was the strongest predictor of their having a colonoscopy (odds ratio, 7.50; 95% confidence interval, 3.40-16.5). Conclusions: First-degree relatives have a low rate of having a colonoscopy but are more likely to have had this procedure if they have strong health motivation. Implications for Practice: Nurses working with CRC patients must develop strategies to increase FDRs' knowledge of, awareness of, and motivation for CRC screening tests. Risk counseling of FDRs during the treatment period might increase screening rates.